The present invention relates to an improved high-voltage level-shift circuit. More specifically, the present application relates to a high-voltage level-shift circuit utilizing a single level-shift switch, preferably a MOSFET.
It is common for high voltage power converters to use level-shifting to control non-ground referenced power switches. A wide variety of methods are available to perform level-shifting, each of which has its own advantages and drawbacks. Typically, however, the need to provide level-shifting results in a more complex circuit regardless of which specific approach it utilized.
Conventional level-shift techniques commonly use a two pulse “set” and “reset” method. In this approach, two high-voltage level-shift transistors are used for the “set” and “reset” signals for turning the high side gate driver on and off. The “set” and “reset” signals are usually provided through a dv/dt filter and then to an R-S latch for storing the on/off state of the high-side gate driver during the corresponding on or off time. This approach, however, has certain disadvantages. After the “set” or “reset” signal is sent to the high-side circuitry and stored in the latch, there is no guarantee that the state of the of the high-side gate driver is the correct state. The low-side circuitry does not receive any signal to verify the state of the high side gate driver. Thus, it is possible that noise, voltage transients or dv/dt disturbances could occur in the high-side circuit causing the latch to change state which may trigger the high-side gate driver to turn the high side switch on or off at the wrong time. This could result in a catastrophic failure of the power circuit depending on the condition of the load. Further, in a half-bridge application, it is critical that the high-side switch, typically a MOSFET, be OFF when the low side MOSFET is ON in order to prevent a direct short across the DC bus. The pulse method does not guarantee that the high side will stay OFF when the low side is ON, and thus, faults may occur.
Accordingly, it would be beneficial to provide a level-shift circuit that avoids the problems identified above.